Electronic repeater



P 2- '-L. w. FRANKLIN 21,280,308

ELECTRONIC REPEATER Filed Dec. 3, 1.958

mvzmon BY. i Q. Tm;

ATTORNEY- Patented Apr. 21, 1942. 1

1 awrence W. Franklin, Hasbrouck Heights, p 'assignor to The Western Union TelegraphCome panyQNeyv York, N. Y., a. corporation of New York 7 Claims.

This invention relates to systems and apparatus for transmitting? and 1 receiving 1 electric currents and more particularly. to vacuum tube repeaters or terminal sets. i i

Heretofore vacuum tube or electronic repeaters for. signaling currents have beenacommonly employed for amplifying continuous waves such as voice currents, and. repeaters: utilizing magnetic relays havebeen' commonly used for shaping and repeating square-ltoppedlwaves such as are used in telegraphy. In certain cases vacuum tube repeatershave' been designedfor repeating comparatively lowfrequencyssignals sent over cables or other channelsof large capacitance, but these repeaters havenot been adapted for regenerating and repeating. high-speed printer signals consisting of code combinations of short, substantially square-topped impulses. The vacuum tube or thermionic valve has been! considered suitable for reproducingfvariable intensity signals without distortion but'the electromagnetic relay has been considered ,moregpractical *for ythe purpose of correcting distortion iniand repeating telegraph or printer signals However .the electromagnetic rela y involves moving parts which are subject to weargand changeximadjustment so that considerable maintenance is required to maintain repeaters, utilizing 1 suchrelays in oper-. ation. Furthermore electromagnetic relays require a definite time for operation and cannot be l employed forrepcating signals above a certain Q 1 ,t 'npplication December s, 1938, Serial No. 243,707

nals owing to changes in line. oryother conditions affecting the signals. a i i Other objects and advantagesofi the invention will appear from the following description of the companying drawingwherein r a; Fig. l is a diagram showing one arrangement preferred embodiments thereof shown in the ac- I of a two-wayelectronic repeaterfor make-ahdf break signals suitable for practicing the invene Fig. 27 is bodying the invention adaptedv to "bewiused; for

rate which isoften reacheddn practice. (If this transmitting; rate 1 is. exceeded or if the relays get out of adjustment the repeater will not function satisfactorily. v i v i In general terms it is the object of the invention to provide a simple and practical repeater or signal-shaping system utilizing f-space-discharge devices such as vacuum tubes or thermionic relays which is capable of regenerating and/or repeating telegraph signals at any desired rate and which does not changev in adjustment or require any maintenanceother than the replacement of worn out parts. c c

Another object of, the invention is to provide animproved two-way electronic. telegraph repeater which may be embodied either in a sys tem for transmitting make-and-break signals or polar signals. i

Another object of the invention is to provide a vacuum tube repeater for high speed printer signals which is adapted to reshape the received signals and in which, the character and bias of the repeated signals may be altered as required by changes in the character of the received sig- "of the received signals is overcome.

repeating polar signals; and

Fig. 3 is a diagram of a further modification adapted for use as aterminal set. I I

A =Q din i th nvent o .thgdire curren telegraph signals are impressed uppn a. space discharge device or vacuum tube. relayl; .A source of alternatingcurrent is provided andt he con 'nection of this source tothe line orvreceiving;

printer is controlledby said relay, the alternating current being rectified andused tojcontrolthe outgoing line or printer. The-repeater is arr, Y ranged to impress impulses of uniform amplitude upon the outgoing line so that the signaling impulses are reshaped and any arnplitude distortion a In the applicationgof the invention two ends of the repeater are electrically 'separat ed as by the alternating currentcoupling transformers between the alternating current source y and the outgoing lines. An interlock is also pro-.

vided whereby the repeaterwill not lockopen when the signal appears in an outgoing side oi. v 3 the repeater which is connected to' one input arranged to repeat side because the repeater is signals in both directions. The mtrlockisprefi erably accomplished by suitably biasing the vacuum tube relay or other element at one input terminal of the repeater when signals from the impressed upon the outgoingcir'cuit.

other input terminalthrough the. repeaterare The invention may also be embodied ina two. way repeater of the duplex type adapted to .re-

peat either make-and-break or polar signals. In

this case no interlock is necessary because of due plexing of the inputand output circuits and, in the .case of polar signals, the impressed'signals are arrangedto reverse the current flowin the outgoing circuit. 1 i

As applied to a. terminal set, a vacuuin tube relay is provided for controlling a local sourceof alternating current which. is rectified and impressed upon a printerbr other receiving tie-' a similar diagram ofya repeater em:

. wi a v way non-duplexed .singleechannel repeater the" vice. Thus the system is arranged to correct distortion of or regenerate the received signals in substantially the same manner as in the repeater circuit.

comprising duplex channels over which signals, may be transmitted simultaneously in both d1- rections. In the single channel two-wayrepeater illustrated, signals may be transmitted in either shown, or one wire of each line may be replaced by a ground connection such as is usual in the art. These lines are normally closed and adapted to be opened to transmit a spacing signal either by conventional transmitting means (not shown) 'atthe remote end of each line to transmit signals to the repeater or, at the repeater to-repeat signals over the respective line circuits,

Assuming that both line circuits are closed to correspondto the rest or marking condition, the

line current flowing throug'h'the space-discharge path between cathode and anode of the normally conductive tube-5| and resistor mhmaintains a positive bias on the control grid H of the spacedischarge device or vacuum tube relay I2 relative to-the potential-of the cathode of said device. The resistor 10 may have a resistance of 300 ohms. The space-discharge device I2 maybe an amplifier tube ofany type adapted to amplify the signal variations impressed upon'theinput circuit thereof or may-be omitted-from the system in ,case the received signals are of sufficient-magnitude. If-th tube -l2is omitted, the grid-cathode connections to resistor 10 -must be reversed. A sharp cut-off voltage amplifier pentode tube, such as thetype 6J7, as shown is preferred in the preliminary amplifier stage since this tube provides stable high gain ampliflcation of signals of the character impressed thereon. Ina similar manner the flow of line current'in the resistance l5 associated with the line L2 maintains a positive bias upon the control grid 16 of the space-discharg device-or vacuum tube relay I! which as shown corresponds in construction and connection to the device'or relay'IZ associated with the line Ll. Since a positive bias is impressed upon 1 the control electrodes of the tubes 12 and ll, both of these tubes are conducting or have alarge anod current flowing through the output circuit thereof. The'connections of the cathode, anode, r

shield grid and suppressor grid of the tubes l2 and l! are conventional and require no further explanation. I

When a spacing signal is received over the line Ll as upon the momentary interruption of the line circuit at the remote "station, the current 1 flowing through the resistor I0 is interrupted, the

of a source-of current 25. 1T

2 direction-but not in both directionssimultaneously, The lines Ll, L2 may be metallic circuits as It will be apparent that the drop of potential across the respective resistors 19, 20 and 2| is utilized for the energization of the elements of the space-discharge device 12. The resistance of said resistors is dependent upon the characteristics of th tube I2. In a similar manner the drop in potential across the respective resistors 22, 23 and 24 is utilized to energize the several elements of a second space-discharge device or vacuum tube relay 3?], the input circuit of which is connected to the output circuit of the tube l2 and includes a series resistor 3|. Th resistor 3| and the similar bias resistors 36, 4| and 41 are shunted by condensers 32, 54, 53 and 43 to filter the rectified alternating current signals into essentially direct current impulses. For ordinary printer signals, the condensers may have a capacity of about 0.00025 mf. if the alternating ourall rentfrequency is of the order of 400 or 500 kilocycles.

Thespace-discharge device or tube 30 connected to the outputcircuit of'tub I2 is arranged to control the connection of asource of alternating current, such as an oscillator .33, to the line L2 in order to repeat the signals received over the line Ll into .said second line. The connection of the source of current 33 to the outgoing line from the repeater or to controlthe current in said line may be accomplished in .various ways, but in accordance with th preferred embodiment of the invention shown, a hexode mixer tube, such as a type 6L1, is employedhavingtwo control electrodes or grids, one of which is connected to the circuit upon which the signalsto be repeated are impressed, and the other is connected through a transformer 34 to the source of alternating current 33 Thus alternating current of a desired frequency is' continually impressed upon one of the control grids of the tube =30 but the spacedischarge path inthe tube presents a high impedance to the passage of this current so long as the other control gridisbiased-to a predetermined negative value whereby under these conditions no alternating current appears inthe output circuit of thetube. However when the negative bias of th first-control electrode of the tube 30 is reduced to approximately zero as a-result of the plate current ofthetube 12 being cut off by the negative voltage on grid H in response to a spacing signal, the alternating current from the source 33 appears in the anode or output circuit of the tube 30 and is impressed through a coupling transformer 31 upon a rectifier ,38. The bias on the firstcontrol grid of the tube -30is also affected by the drop in potential across the bias resistor 3|, as will b explained below.

The transformer 31 is provided with two secondary windings as shown, and may be an aircore radio frequency transformer if the source of current 33 is of relatively high frequency, for example of the order of 450 kilocycles. The employment of a relatively high frequency of this order is preferred as simple and efficient radio frequency transformers for this frequency may be employed and the apparatusis able'to repeat signals of much higher frequencies than have heretofore been'possible, for example, of several thousand cyclesper second. However, the source 33 may be of a frequency of threeor four thousand cycles per second, in'which'case an ironcore audio transformer would be employed in place of the radio frequency transformer 31. Under these conditions the repeater would respond to signals of several hundred cycles-per second.

It will be apparent that, as pointed out above, 1

' adjustmentof this character is not essential but I in cases of severeline leakage a readjustment of the operating point of tube I2 by means of, resistor I9 is desirable; When the tube comes non-conductive as described, in response to a spacing signal, the negative bias on the first control grid of the tube 30 is reduced owing to the drop in potential across the coupling resistor 28 .in the outputcircuit of the tube I2 being reduced, and alternating current from the source 33 is impressed upon the rectifier 38 by the tube 30 and the transformer3l.

' The rectifier 38 is shown as a double diode rectifier, for example of the 6H6 type, having two separate rectifying paths connected to separate secondary windings of the transformer 31. Obviously if desired separate 'rectifiers might be employed. The rectified current, caused by a spacing signal in the line LI, from one secondary winding of the transformer?! is impressed across resistor 4I, filtered by condenser 53, and upon the grid-cathodecircuit of a space-discharge device or vacuum tube 40 which is normally conductive as long as the rest or marking condition obtains in the line LI. The tube 40 is shown as a beam power amplifier of the SL6 type, for example, since this tube is adapted to handle the current required in normal telegraph operation but any other suitable amplifier tube may be employed. Upon the flow of alternating current from the source 33 in the upper secondary winding of the transformer 31, a rectified current flows through the resistor 4| in such a direction that the drop of potential across said resistor biases the control electrode of the tube 40 negative to cut off, thereby interrupting the current flow in the line L2 and transmitting a spacing signal corresponding in duration to the spacing signal received over the line LI. It will be apparent that the lines LI and L2 are electrically separated from each other by means of the couplingtransformers 31 and52,

the received signalsbeing converted to alternating current signals, transmitted through the windings of the transformers and then rectified and impressed upon the outgoing line. Anydistcrtion in the received signals is corrected since the magnitude and wave shapeof the signals transmittedover the line L2 are independent of variations in the received signals resulting from the inductance and capacity of the line LI or from inductive interference so. thatregenerated signals are transmitted from the repeater over the line L2. It will be also apparent that when the line LI is reclosed, the energizationof transformer 31 from the source 33 is interrupted and the bias on the tube 40 is removed, thereby reestablishing the flow of current in the line L2.

In order to prevent the transmission of the spacing signal over the line L2 as described above from being reflected back into the repeater through the discharge device or relay 45, corresponding ,to the discharge device 30, which would render the repeater inoperative, the lower secondary winding of the transformer 31 and the associated rectifying means are arranged to bias disconnected from the line LI.

the vacuum tube relay 45 in such a manner as to maintain the alternating current source 46 The source. of alternating current 46 corresponds to the source 33 associated with the vacuum tube 30 and a single source of alternating current may be employed for both relays 30..and 45. vThe flow of rectified current through the resistor 41 corresponding to the resistor 3|v associated. with the vacuum tube relay 30 applies anegative bias to one control electrode of the vacuum tube 'to maintain said tube Anon-conductive irrespective of'the change in bias thereof produced by the firststage amplifier tube I'I. Thus the inter: ruption ofthe current in-the line L2 for repeating a signal to a remote station does not affect the part of the repeater which is normallyoperative to repeat spacing signals received over'the line L2 to the line LI. i j

The lower half of .the repeater comprising the space-discharge devices or vacuum tubes I1, 45, 50 and 5| and their associated elements corresponds precisely tothe upper half of said repeater and therefore a detailed description of the operation thereof to repeat signals from the line L2 to thelineLI is unnecessary. It will be apparent that if a spacing signal is received over the line L2, this signal is amplified by the tube I'I, translated into an alternating current signal by the tube :45 and the resulting signal rectified and impressed upon the line LI through the tubes 50 and 5| in the same manner as described above in connection with the repeating of signals from the line LI to the line L2 by the discharge devices I2, 30, 38 and40. C I

The transformer 52 corresponds to the transformer 31 ofthe other half of the repeater and serves to insulate the line L2 from the line LI for repeating signals from L2 to LI. When a spacing signal is impressed upon the amplifier II,

, the alternating current from the source; 46 is impressed upon transformer 52, is rectified by the rectifier 50 and causes a potential drop across the terminals of the resistor 3| to bias the first,

circuits where the interference level is high relative to thesignal level. The action of this circuit is fully described in the copending application of F. E. dHumy et al., Serial No. 114,460, filed December 5, 1936. The value of the resistor I8 is dependent on the value of resistor I0 and may be 5000 ohms where resistor I 0 is 3000hms. The higher the value of III, the higher I8 must be in proportion. The capacity of condenser 26 should be such that in combination with I 8, a time-constant of the same order as the minimum signal length is obtained. For example, the condenser would have a capacity of from 0.5 to 1 mi. for a signal frequency of about cycles per second.

Among the outstanding advantages of the repeater described may be mentioned the high rate of signal transmission that may be utilized and the'absence of all mechanical or movingparts requiring maintenance and adjustment; In

many .cases where repeaters .using mechanical relays are employed, it is often necessary to bias the receivingrelay in one direction due to the transmitting relay being biased .in'the other direction, whichadjustments may be marginal and difficult .to maintain. .In any event, a repeater employing mechanical relays requires continualsupervision and maintenance, .which is avoided by thepresent invention. Furthermore, in the described'repeater incoming signals are received as a voltage across a series resistor in a line circuit so that there is .no inductance in the line as in the case of a repeater employing mechanicalmelays havingcoils in the line circuit. In this manner the distortion resulting from additional inductance in the line circuit is avoided.

The principles embodied in the repeater shown in Fig. 1 may be applied to systems utilizing polar or two-element .(positive and. negative) signals and may be embodied in repeaters associated with duplex circuits as well as in a single channel system such as illustrated in Fig. 1. Fig. 2..shows. a .repeater adapted .for repeating and regenerating .polar signals from one duplex line L3 to a secondduplex line L4 and vice versa.

The. duplex channel L3 is of the bridge type having two resistors .andBl connected between .the line circuit .and the artificial line. Thusthe polar signals received over the west line circuit .appear as opposite voltages across the outer terminals of the series resistors 60 and 6|, whereas .the signals transmitted from the repeater west are applied to the -midpoint of the bridge through the conductor .63, and have no effect upon the total potential drop .across the tworesistors. In a similar manner .the duplex system associated, with .the line L4 .comprises resistors 54. and to .the midpointof .which is connected conductor .66 for repeating :signals from the .repeater feasti The operation of therepeater shown. in Fig. 2 is similar inmost ,respects to .that .shown in Fig. I. The discharge device orprimary amplifier tube. 10, which may be of .the .6J7 typeas shown, .is normally'conducting during. rest -or marking conditions duringwhich it is .assumed that positive potential impressed upon the control grid of said discharge device 10 maintains. a current flow in the output circuit ofsaid. device. Consequently, the drop of .potential across a resistor :H in said output circuitthereof maintains the first control grid of the.space-discharge device or vacuum tube 12, for example of the 6L7 type, negative, thereby interrupting .the .flow. of alternating current from the source J3 .to the transformer .14 and the second control grid from appearingin the output circuit of the discharge device 12. :However,: when a spacingsignal is received andtheipolarity of the signal potential.

across the bridge of the.duplex .circuit is reversed, the control-gridof thedischarge .device 10 becomes negative,.the potential drop across the resistor TI is reduced and ,the discharge .device 12 becomes conductiveto alternating current from the source '13. The flow of-alternatingcurrent through the .primary winding of the transformer :11 .in.the output circuit of the discharge device 1-12. generates a..direct current potential across the terminals. of :theresistor l8 whichis connected in series with a double-wave rectifiertube 19, for example of the 6H6 .type, to the secondary winding :of said transformer :11. The potential dropacrossresistor 18 issrnoothed by. thetiilter .circuitu80. and :impressed uponrthecontrol electrode ,of the space-discharge device 82. The-discharge device 82 is normally conductive during the rest or marking condition, but is biased to cut-off by the potential drop in the resistor -18 when spacing signals are received over the line L3. The discharge devices 82 and 85, which may be of the SL6 type, jointly control the .polarity of the signals impressed upon the line L4 at the repeater, as will be explained.

It will be apparent that as long as the spacedischarge device 82 is conductive, a path of low resistance is provided from negative battery through the cathode and anode of the discharge device 82, the resistor 83, the conductor 66 and the resistor 64 connected to the line L4. In this case it will be seen therefore that as long as positive or marking conditions persist on the line L3, the line L4 is maintained negative so that the repeater effects a reversal of the character of the signals, positive marking signals being transposed into negative marking signals. Similarly when a spacing signal is received over line L3 applying negative potential to the grid of the amplifier tube ll], as described above, the spacedischarge device or tube 12 is biased to cut-off thereby disconnecting the negative battery associated with the cathode of said tube from the line L4 and said line is connected through a cathode and anode of the space-discharge device or tube to positive battery. The tube 85 is nonconductive as long as the line current flows through the resistor 83 and the cathode-anode circuit of the tube 82 since the drop in potential in the resistor 83 biases the control electrode of the tube 85 to a negative potential with respect to its cathode. In this manner the marking potential on the line L4 is discontinued and positive or spacing potential applied for the duration of the negative spacing signal received over the line L3.

It is not necessary to reverse the polarity of the regenerated signals unless desired as the connections of the line L3 and the artificial line associated therewith may be reversed if desired in order to invert the response of tube 10 to the polarity of the received signals. In a similar manner if a reversal in the polarity of the signals corresponding to marking and spacing conditions in the line L4 is desired, the connection of the preliminary amplifier tube 86 to the outer terminals of resistors 64 and 65may be reversed in order to render the tube responsive to signals of the opposite polarity or the connections to the line L4 and the corresponding artificial line AL may bereversed as described above.

The bottom half of the repeater shown in Fig. 2 corresponds precisely to the upper half of said repeater, the tubes 86, 8'1, 88, 89 and 9D corresponding inarrangement and function to the tubes '10, 12, 19, 82 and 85, respectively. It will be apparent that this portion of the repeater is adapted to repeat and regenerate signals received over the line L4 to the'line L3 in the same manner as the upper half of the repeater repeats signals from the line L3 to'the line L4.

Fig. 3 illustrates how the repeater shown in Fig. 2 may be split and utilized as a terminal set with the tubes 10, 12, 19 and 82 being connected to the line L3 in exactly the same manner as shown in Fig. 2. The printer is connected to be operatedby .the make-and-break signals in the output circuit of the tube .82, the polar signals received over the line L3 being converted into makeeand-breaksignals and regenerated by the elements .of xthe'terminal-set in the same mannor as in the repeater. A transmitter 96 is shown associated with the line L3 for transmitting polar signals over said line. In view of the similarity between the elements of the terminal set shown in. Fig. 3 and the repeater shown inFig. 2, it is believed that no further description of the terminal set is necessary.

It will be apparent that the described signal repeating and regenerating means, having no moving mechanical elementsis operative at almost unlimited transmitting rates and requires no adjustment or maintenance. It is operative to regenerate the wave shape of high-speed printer signals, which are usually substantially squaretopped Waves, and correct the distortion resulting from the characteristics of the line circuit and from interference. The characteristics of a repeater embodying the invention are thus of practical value.

Various modifications of the specific systems shown and described for the purpose of explain ing the invention will occur to those skilled in the art and may be made without departing from the scope of the invention as set forth in the appended claims.

I claim:

1. In a telegraph system, two lines, means for impressing code telegraph signals on one of said lines and a repeater for relaying said signals to the other line, said repeater comprising an oscillation generator, a thermionic relay having input and output circuits, a rectifier having its output circuit connected to said other line, a connection through said rectifier on said other line corresponding to those impressed on said thermionic relay.

2. In a telegraph system, two lines, means for V impressing high-speed direct current printer signals on one of said lines and a repeater for relaying said signals to the other line, said repeater comprising an oscillation generator of relatively high frequency compared to the frequency of said signals, a vacuum tube relay provided with a cathode, an anode and two control electrodes, input and output circuits for said tube associated with the respective lines, said input circuit including one :of said control electrodes and a connection from said oscillation generator to the other of said controlelectrodes.

3. In a telegraph system, a line, means for impressing high-speed direct current printer signals on said line and means for regenerating said signals, said last-mentioned means comprising a space-discharge device provided with a cathode, an anode and two control electrodes, an oscillation generator connected to one of said control electrodes, means for impressing said printer signals on the other control electrode and thereby driving said space-discharge device from beyond cut-off .to the condition of normal space-- rent to either circuit in accordance with signals received over the other circuit and means responsive to the reception of spacing signals at the repeater for looking out the repeater with respect to transmission in the oppositedirection from which said spacing signals are to be transmitted.

5. In a telegraph system, two lines and a repeater for repeating and regenerating signals from one of said lines to the other line, said repeater comprising a source of alternating current, rectifier means and means for controlling the connection of said alternating current source and said rectifier means to either of said lines in accordance with signals received over the other line.

6. In a telegraph system, a line, means for impressing high-speed direct current printer signals on said line, receiving means and means con nected to said line and said receiving means for regenerating said signals, said last mentioned means comprising an oscillation generator of rel atively high frequency compared to the frequency of said signals, a space-discharge device of the mixertype provided with a cathode, an anode and two control electrodes, a connection between one of said control electrodes and said line, a connection between the other of said control electrodes and said oscillation generator, and a connection between the cathode-anode circuit of said device and said receiving means.

7. In a telegraph system, a line, means for impressing high-speed direct current printer signals on said line, receiving means responsiv to said signals, a source of alternating current, and a space-discharge device between said line and said receiving means, said space-discharge device being provided with a cathode, an anode and two control electrodes, one of said control electrodes being connected to said line and the other to said source of alternating current, input and output circuits for said space-discharge device including said one of said control electrodes connected to the line and said anode, respectively, and. means whereby alternating current signals are generated from said source in the output circuit of said space-discharge device corresponding to the direct current printer signals in said line. i

LAWRENCE W. FRANKLIN. 

